1. Field of the Invention
The present invention relates to a processing method and a processing apparatus of organic wastes, and a processing method and a processing apparatus of inorganic wastes.
2. Description of Related Art
In recent years, disposal of organic wastes including resin such as plastic containers or polyvinyl chloride, or radioactive materials is becoming a big problem. Conventionally, the organic wastes are disposed of by incineration, however, with such a processing method, there are such problems that hazardous materials such as dioxin, nitrogen oxides and the like are generated, and a large scale apparatus recovering these hazardous materials is required.
In addition, inorganic wastes in the field of atomic energy contain a huge volume of sodium nitrate other than radioactive materials. Thus, radioactive materials are buried with sodium nitrate as a solidified body in a processing field located underground. As a result of the recent study of the underground environment, it is reported that the underground is low in its oxygen partial pressure, nitrate ions are likely to become ammonia accordingly. As the result, it is pointed out that there is a likelihood of radioactive material such as plutonium and the like forming a complex with ammonia and being eluted from the solidified body.
Recently, as a method decomposing an organic material, a method employing water under a high temperature and a high pressure (supercritical water) exceeding the critical point of water (temperature: 374.degree. C., pressure: 22.1 MPa) is attracting attention.
The supercritical state denotes a state of a substance which is under a temperature and a pressure exceeding the critical temperature and the critical pressure both of which are the physical quantities inherent to individual compounds, and a substance in this state is called a supercritical fluid.
A method is known in which an organic material and a fluid containing water and oxygen are mixed and the organic material is oxidized/decomposed under a supercritical state exceeding the critical point of water ("Organic material oxidation method in water exceeding supercritical point", Japanese Patent Application No. Sho-56-68414, Registration No.1551862). The supercritical water, being intermediate of liquid and gas in its properties and capable of being mixed with an organic material and oxygen at an arbitrary ratio, can decompose the organic material effectively in a short time.
However, in the supercritical state, since solubility of inorganic materials is remarkably small, there occurs a problem that inorganic materials contained in the organic wastes precipitate on the surface of the reactor, thereby plugging the reactor. The solubility of the inorganic oxides being particularly small, such trouble is likely to be caused accordingly.
For instance, when wastes from an atomic power plant are processed, because of precipitation of radioactive materials, handling is not easy and huge cost is needed for maintenance of the waste processing apparatus.
Therefore, development of a method and an apparatus of decomposing organic wastes by making use of the supercritical state without precipitating inorganic substances is expected.
Further, as described above, if ammonia exists in a solidified body, there is a likelihood of the radioactive materials such as plutonium being eluted from the solidified body. Therefore, development of a waste processing method and an apparatus which, even when the wastes including only inorganic materials are processed, can prevent the nitrate ions from being contained in the solidified body by converting the nitrate ions or nitrate salts to nitrogen, is expected.